Reduction of the loss of zinc by its reaction with oxygen in galvanized steel and batteries

ABSTRACT

A non-porous Zn 2+  conducting inorganic lamellar layer is formed on the zinc coating of galvanized steel or on a zinc anode of an electrochemical cell. The layer reduces the rate of the unwanted chemical reaction of zinc and oxygen but allows desired electrochemical reactions underlying the cathodic protection of the steel and the efficient utilization of zinc anodes in electrochemical cells, e.g., a physiological buffer solution or serum as their electrolytes. The ion conducting non-porous lamellar layer having a hopeite phase Zn 3 (PO 4 ) 2 .4H 2 O may be formed spontaneously on, e.g., NAFION® coated zinc anodes discharged in neutral pH saline phosphate solutions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser. No. 60/718,158, filed Sep. 15, 2005, the contents of which are incorporated by reference herein in its entirety.

The U.S. Government may own certain rights in this invention pursuant to the terms of the Naval Research Grant (00014-021-1-0144).

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the prevention or alleviation of loss of zinc in anodes by its reaction with oxygen. The prevention of such loss is of essence for high the utilization efficiency of the zinc in galvanized steel. Here the zinc cathodically protects the steel against corrosion. Protection of metal corrosion is of particular use in batteries with zinc anodes, particularly batteries having small, high surface to volume ratio, zinc anodes.

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is described in view of utilization of the zinc anodes in galvanized steel and in batteries.

Galvanized steel is one of the most widely used structural metals. For example, bodies of automobiles are made of galvanized steel. Galvanized steel includes, in addition to its steel, which provides strength and other desired mechanical characteristics, a layer of zinc, which protects the structural steel against corrosion. The zinc is usually phosphated. In the phosphating process, hydrated zinc phosphates are formed on the surface of the zinc. Galvanized steels are generally made by dipping the steel in molten zinc, a method assuring excellent bonding of the zinc to the steel. Alternatively, galvanized steels are made by electroplating zinc on the steel. Other methods, such as high rate evaporation, sputtering or electroless plating are also possible.

Generally, the process of steel corrosion is initiated by an electrical potential difference between regions of the surface that come in contact with an electrolyte (e.g., moisture condensing from the air). An electrical current begins to flow and iron ions are formed that result in loose flaky rust (i.e., iron (III) oxide). The electrons generated in the Faradaic reaction of zinc keep the iron reduced to the metal, i.e., prevent its oxidation to iron oxide, by shifting the initial corrosion reaction Fe

Fe²⁺+2e⁻ to the left. Techniques currently used in the art include a zinc coating that is metallurgically bonded to the surface and protects against corrosion by shielding the base from the atmosphere and acting as a sacrificial protection layer that is gradually consumed (e.g., the zinc is more electronegative than iron or steel and provides cathodic protection).

The zinc coating may be applied by hot dip galvanizing, electroplating, evaporating or other methods known in the art. For example, one process of zinc coating is a hot dip galvanizing process that involves: cleaning (i.e., generally an alkaline solution) and pickling (i.e., a pickling solution is generally hydrochloric or sulfuric acid) at free the surface of dirt, grease, rust and scale; a preflux step to dissolve oxides formed on the surface after pickling and to prevent further rust formation; a coating step of immersion into molten zinc; and a quenching step. A patina of zinc oxide, zinc hydroxide, and zinc carbonate will form on the zinc surface.

The zinc coating of galvanized steel cathodically protects the steel against corrosion. When the steel is cathodically protected, the oxidative corrosion of steel, evident, for example, when the steel is rusting, is slowed or prevented, while zinc of the coating is sacrificially oxidized to Zn²⁺. The Zn²⁺ is usually precipitated, for example, as a carbonate, oxide, or, when an anion is present, as a zinc salt of the anion.

After the steel is galvanized, it is often phosphated. The phosphating process involves the immersion of the steel in a phosphate containing bath. Phosphating, or phosphatizing, are known to produce films containing, or having, hopeite; however, as was shown, for example by Miles in U.S. Pat. No. 4,330,345, the structure, morphology, and size of the crystallites of different phases in the films affect their properties.

It is well known that phosphating often produces a film containing, or having, hydrated zinc phosphate, which protects the protective zinc. The hydrated zinc phosphate often is, or may include, some hopeite, the chemical composition of which is Zn₃(PO₄)₂. 4 H₂O.

Numerous methods and formulations of compositions for phosphating the zinc layer of galvanized steel and forming on it hopeite containing films are known. A few, such as those of T. Sugama, U.S. Pat. No. 5,604,040 and T. Nakayama et al., U.S. Pat. No. 6,478,860, disclose adding to the phosphating solution, about 0.5 to 5.0% by weight of water soluble polycarboxylates, such as polyacrylates acid, polymethacrylate and nucleating components; however, the polyanions were not applied as films on the zinc anodes, unlike in the method disclosed here.

When Zn cathodically protects steel, the electrons generated in the anodic reaction Zn→Zn²⁺+2e⁻ reverse the initial step of the corrosion reaction of iron, Fe→Fe²⁺+2e⁻, the iron being poised now at the thermodynamic potential of the zinc anode, where it could, instead, be plated, Fe²⁺+2e⁻→Fe. The necessary electrochemical half cell reaction, Zn→Zn²⁺+2e⁻, can not proceed unless microscopic charge neutrality was maintained in the electrooxidation of the Zn. Maintenance of charge neutrality was thought to require either transport of electrolytic solution phase anions to the zinc anode or electrolytic solution phase transport of Zn²⁺ from the anode. An electrolytic solution could not access, however, the anode surface in absence of defects, such as pores, in the film on the zinc anode, which was mostly hopeite in galvanized steel, and zinc oxide, or hydrated zinc oxide, in battery anodes. When pores, or other solution access providing defects are present in a film, dissolved oxygen also reaches the electrochemically active metallic zinc surface. Because oxygen reacts non-Faradaically with the zinc, it reduces the utilization efficiency of the zinc that cathodically protects the steel in galvanized steel, or is available for the desired cell reaction in a battery.

The foregoing problems have been recognized for many years and while numerous solutions have been proposed, none of them adequately addresses all of the problems in a single device.

SUMMARY OF THE INVENTION

The inventors discovered materials and methods for maintaining microscopic electrical neutrality at an operating zinc anode, without providing access of an aqueous electrolytic solution to the surface of the zinc anode. Usually, the maintenance of microscopic electrical neutrality requires access of liquid electrolyte to the zinc anode through pores in the film on the zinc anode passivating it against rapid reaction with dissolved oxygen and/or water. After the zinc is phosphated, access of ions to or from the zinc must be provided. Most commonly, the access is through pores or other defects in the phosphated zinc layer, filled with the electrolytic solution. The solution, including that in the pores, dissolves oxygen, which oxidizes the zinc. The oxidation of zinc by oxygen is an undesired non-Faradaic reaction, reducing the coulombic efficiency of zinc utilization in the cathodic protection of steel. The inventors increased the zinc utilization efficiency of zinc anodes operating in oxygen containing environments by forming in their phosphating process a substantially non-porous Zn²⁺ ion conducting hopeite film allowing the discharge of zinc anodes in absence of contact between the aqueous solution and the electroactive zinc. Specifically, the inventors discovered that pore-free crystals of hopeite can be solid state conductors of Zn²⁺ and possibly also of other, ions. The transport of Zn²⁺ through solid hopeite allows the desired Faradaic reaction Zn→Zn²⁺+2e⁻. At the same time, because hopeite does not dissolve oxygen and because oxygen does not permeate through hopeite, the film prevents the undesired non-Faradaic reactions 2 Zn+O₂→2 ZnO and/or 2 Zn+O₂+H₂O→2 Zn(OH)₂.

It was found that the coulombic efficiency of zinc utilization is highest when the zinc anodes are coated with non-porous or minimally porous hopeite. Minimal porosity and good Zn²⁺ conductivity are best achieved when the hopeite crystals on the Zn anodes are large but thin, which is the case when the crystals are lamellar. In general, the widths and the lengths of the hopeite lamellae are greater than about 2 micrometers, more preferably they are greater than about 5 micrometers and most preferably they are greater than about 10 micrometers. The ratio of their height, or thickness, to their width or length is less than about ⅓, is preferably less than about ⅕ and is most preferably less than about 1/10.

The inventors further discovered that the Zn²⁺ conductive hopeite lamellae are produced on Zn anodes discharged in safe and easy to handle, environmentally friendly, solutions. The preferred solutions are dilute, neutral or near neutral pH, phosphate solutions, containing alkali metal or tetraalkyl ammonium salts, of which simple Na⁺ or/and K⁺ salts are preferred, and the simplest and least expensive Na⁺ salts, NaCl or Na₂SO₄, are most preferred.

To produce the densely packed, non-porous film of large lamellar hopeite crystals, the inventors pre-coated their Zn anodes with a thin film of a cation exchanger. They hypothesized, that in combination with the Na⁺ ions in the solution, which compete with the Zn²⁺ ions for the anionic sites of the cation exchanging film, the cation exchanger controls the relative rates of hopeite nucleation and growth of the hopeite crystals, which depend on the local Zn²⁺ concentration. However, it should be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention.

The pre-coated cation exchangers can be polycarboxylates, such as polyacrylates or polymethacrylates, polysulfonates or polyphosphonates. Of these, polysulfonates such as NAFION® and other thermostable and chemically stable polysulfonates, useful in membranes of acid electrolyte fuel cells, described, for example, in U.S. Pat. Nos. 6,423,784, 6,559,237, 6,649,295, 6,833,412, 7,060,738 or 7,060,756, are preferred.

After the inventors discovered that the non-Faradaic corrosion of a fluorinated sulfonic acid polymer (e.g., NAFION®) coated zinc anodes is drastically reduced at neutral pH both in a physiological saline buffer solution (pH 7.4, 0.15 M NaCl, 20 mM phosphate) under air and also in serum under air, when the anodes are overgrown by large non-porous lamellae of hopeite [Zn₃(PO₄)₂.4H₂O] which are impermeable to O₂, they demonstrated the operation of a hopeite protected low rate zinc anode in a potentially implantable in-vivo power supplying electrochemical cell. The cell, using as an exemplary cathodic reactant silver chloride, also uses, optionally, a body fluid as its electrolyte. The use of a body fluid as the electrolyte obviates the requirement of a case, and allows the formation of in-vivo electrochemical cells having merely of an implanted, miniature, zinc anode and a miniature silver chloride, or other, cathode.

In the context of potentially implantable biofuel cells, the inventors observed that the Zn²⁺ conducting hopeite protected against non-Faradaic corrosion Zn fiber anodes in calf serum, an exemplary body fluid of an animal. A miniature Zn |serum| Ag/AgCl cell, made with a fine, about 100 micrometer diameter and about 2 cm long Zn fiber anode, operated at about 1.00 V and about 13 μA cm⁻² for about 2 weeks, at about 60% zinc utilization efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:

FIGS. 1A, 1B and 1C are schematics of the preparation of the coated zinc anodes of the present invention;

FIGS. 2A and 2B are optical micrograph images of the tips of the Zn anodes of the present invention;

FIG. 3 is a plot showing the identity of X-ray diffraction patterns of the present invention and a commercial Zn₃(PO₄)₂.4H₂O;

FIGS. 4A, 4B and 4C are images of the showing the dimensions and morphologies of the coatings formed at the completion of the discharge on the zinc anodes;

FIG. 5 is an electron micrograph of the non-porous hopeite lamellae overgrowing the coated zinc fiber anode;

FIG. 6 is a plot illustrating the time dependence of the potential of the discharged Zn anode discharged at a current density of about 13 micoamperes per square cm;

FIG. 7 is a cyclic voltammogram that is indicative of the blockage of O₂ transport to the Zn anodes;

FIG. 8 is a structural model of hopeite Zn₃(PO₄)₂.4H₂O; and

FIG. 9 is a schematic diagram of a case-less miniature Zn(NAFION®)—AgCl battery operating in the subcutaneous interstitial fluid.

DETAILED DESCRIPTION OF THE INVENTION Glossary of Terms

Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.

Bath refers to a solution that directly contacts the substrate. The term “Bath” is not intended as a limitation of the manner of application of coating which generally can be applied to the substrate by various techniques, e.g., nonexclusive examples include immersion, dipping, spraying, placing the substrate into the bath, intermittent spraying, flow coating, and combined methods such as spraying-dipping-spraying, spraying-dipping, dipping-spraying or combinations thereof.

Electrolyte denotes a usually electronically insulating substance through which an electric current is carried through the motion of ions.

Steel: An alloy of iron, containing carbon, and, optionally, other, usually metallic or semiconducting, elements.

Cathodic protection means the reduction of the rate of oxidative corrosion of a metal, such as steel, by the application of a reducing potential. Although the potential may be applied using a source of DC or rectified AC power, it is more convenient to apply it by electrically contacting the protected metal, such as steel, with another metal having a more reducing electrovhemical potential in the solution in which both metals are immersed, such as zinc or an alloy of zinc. When the zinc is in electrical contact with the steel, the steel is cathodically protected by the zinc.

Zinc or Zn: In addition to the metal itself, which is generally most preferred, the term includes also alloys and mixtures of zinc, where the atomic fraction of zinc is not less than about 0.5, is more preferably not less than about 0.7, and is most preferably greater than about 0.9. Exemplary metals in alloys or mixtures of Zn are Fe, Mn, Co, Ni, Ca, Mg, and/or Ti.

Galvanized steel: Steel, preferably steel sheet, coated with zinc. The coating is, optionally, by dipping the steel in molten zinc. Alternatively, the zinc can be deposited on the steel by other means, for example by electroplating.

Zinc anode: A zinc comprising electrode, some or all of its zinc capable of undergoing the reaction Zn→Zn²⁺+2 e⁻. The zinc coating of galvanized steel and zinc electrodes of batteries are examples of zinc anodes.

Faradaic reaction: An electron flux producing or consuming electrochemical process. Because microscopic charge neutrality is maintained in Faradaic reactions, in addition to the flow of electrons, Faradaic reactions also require transport of ions. In contrast to a Faradaic reaction, a non-Faradaic reaction does not produce or consume an electron flux.

Corrosion of zinc means the usually undesired non-Faradaic reaction of zinc with oxygen and/or water. Such corrosion reduces the zinc utilization efficiency.

Zinc utilization efficiency, coulombic efficiency, and coulometric efficiency are used interchangeably to denote the ratio of the generated charge (e.g., by a discharging Zn anode of a battery) to the consumed charge, which is the charge passed through an electrode in the electroplating of zinc. It is the ratio, optionally expressed as a percentage, of the electrical charge stored in a charged electrode that is recovered during its discharge. Generally, current inefficiencies arise from reactions other than the intended electrochemical reactions taking place, or side reactions consuming the electrodes. The three terms all mean the ratio of the charge produced in the Faradaic reaction whereby an electrode is consumed and the sum of the of the Faradaic and non-Faradaic reactions by which the same electrode is consumed. For example, a zinc anode is consumed by the Faradaic reaction Zn→Zn²⁺+2 e⁻ and by the non-Faradaic reactions 2 Zn+O₂→2 ZnO or 2 Zn+O₂+2 H₂O→2 Zn(OH)₂.

When the current efficiency, electrode utilization efficiency or coulombic efficiency is 1.00 than about 2 Faradays, or about 2×96485 Coulombs, are produced per about 65.4 grams of zinc. When only the non-Faradaic reaction takes place, the charge produced is nil. In galvanized steel, the zinc utilization efficiency defines, for example, the period over which the steel is cathodically protected when in absence of cathodic protection the steel would corrode at a given rate.

Zinc, Zn, and zinc anode are synonymous and include alloys in which the fraction of Zn atoms exceeds 0.5, preferably 0.7 and most preferably 0.9.

Oxygen means the dioxygen molecule, O₂.

Zn₃(PO₄)₂.4H₂O and hopeite are synonymous and include compounds or phases Zn_([3-x])M_(x)(PO₄)₂.4H₂O that conduct Zn²⁺ and/or M²⁺ ions, where M²⁺ is Fe²⁺, Co²⁺, Mn²⁺, Ni²⁺, Ca²⁺ and/or Mg²⁺.

Lamallae and lamellar refer to hopeite crystals the thickness of which is smaller than their width or length. Typically, the thickness of the lamellar crystals is less than about ⅓^(rd) of their width or length. Preferably, it is less than about ⅕^(th) of their width or length; and most preferably it is less than about 1/10^(th) of their width or length.

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The terminology used and specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

The electrodes of the present invention comprise an at least partially conductive substrate having a Zn layer deposited onto the at least partially conductive substrate. The at least partially conductive substrate then has a sulfur or phosphorus containing polymer coating and a layer of hopeite deposited thereon. The electrodes of the present invention also include a Zn anode on an at least partially conductive substrate, having an external layer of hopeite crystals.

The present invention also provides a method of preparing an electrode by depositing a metal layer onto a substrate, applying a cation exchanging polymer-coating layer onto the metal layer and depositing a layer of hopeite onto the polymer coating layer. The invention further provides a solid electrolyte film, formed generally of non-porous hopeite lamellae that are impermeable to molecules, particularly to oxygen. The solid film conducts Zn²⁺ and/or other ions. The film is impermeable to oxygen because oxygen is insoluble in hopeite. Therefore, the present invention provides numerous uses for the protection of functional electrode surfaces from oxygen.

The invention additionally provides a non-porous film having or including hopeite lamellae on a zinc surface, preventing the zinc from rapidly reacting with oxygen and/or moisture in air. The zinc may be the on steel or any other metal surface that could corrode by reacting with oxygen, e.g. cast iron, wrought iron, or copper and its alloys. The invention also provides for efficient use of zinc following its treatment with a phosphate containing solution, such that a non-porous lamellar hopeite film is formed on the zinc surface. The inorganic hopeite crystals conduct Zn²⁺ ions and unlike other films on galvanized steel are non-porous and impermeable to liquid electrolytes and/or oxygen.

The inventors consider as a particularly important the application of their discovery of Zn²⁺ ion conduction in an oxygen impermeable inorganic solid, such as hopeite, the improvement of the coulombic efficiency of zinc utilization in the cathodic protection of structural alloys, particularly of galvanized steel.

An exemplary process leading to greater utilization efficiency of the zinc in galvanized steel, would start with coating of the zinc surface with a polymer. The polymer is preferably a cation exchanger, and it is most preferably a cation exchanger with sulfonate and/or sulfonic acid functions. Cation exchangers of which acidic fuel cell membranes are made are preferred. These include, for example, NAFION® and other perfuorinated, fluorinated and non-fluorinated cation exchangers, including, for example, those described in U.S. Pat. Nos. 6,423,784, 6,559,237, 6,649,295, 6,833,412, 7,060,738 or 7,060,756.

A solution or dispersion cation of the cation exchanger, when necessary containing an added crosslinker, could then be applied to the galvanized steel, for example, by spraying, hot spraying, brushing or dipping. Following the application, the film is cured or dried in such a way that the film is rendered substantially insoluble in water at ambient temperature. It is advantageous for forming the desired Zn anodes to coat these with a film of a cation exchanging polymer, such as NAFION®. It is preferred that the resulting film, formed after drying or curing, be of about uniform thickness. The thickness of the useful films is usually greater than about 10 nm and is less than about 100 micrometers. The preferred thickness of the dry films is between about 50 nm and about 1 micrometer. Optionally, after their drying, the films may be baked or otherwise heated at a temperature greater than about 90° C. and less than about 200° C., preferably greater than about 110° C. and less than about 150° C. for a period that is typically not less than about 30 seconds and is not greater than about 24 hours.

The now polymer coated galvanized steel would then be exposed to a solution containing a phosphate and an alkali metal salt. The source of phosphate ion may be any material or compound known to those skilled in the art to ionize in solutions to form phosphate anions such as phosphoric acid, alkali metal phosphates such as monosodium phosphate, monopotassium phosphate, disodium phosphate, divalent metal phosphates and the like, as well as mixtures thereof. The preferred alkali metal salts are salts with anions the zinc salts of which are readily water soluble, their solubility exceeding about 0.1 M at 25° C. Examples of useful salts are salts with Na⁺ or K⁺ or tetraalkyl ammonium, e.g. tetramethyl ammonium, cations and anions like Cl⁻, Br⁻, SO₄ ²⁻ or NO₃ ⁻. The most preferred salt is NaCl. The concentration of the salt is generally greater than about 50 mM and less than about 3 M, a concentration greater than about 0.1 M and less than about 1 M being preferred. The pH range of the phosphate containing solution is generally less than about 10 and greater than about 4. The phosphate concentration in the solution is generally greater than 5 mM and less than about 500 mM. The preferred phosphate concentration range is between about 10 mM and about 200 mM. The phosphate may be added as an alkali metal salt, such as sodium or a potassium salt, optionally as a mono or dibasic salt.

Although the desired hopeite film is expected to form spontaneously upon immersion of the galvanized steel in the aerated phosphate and salt containing solution, the formation of hopeite could be accelerated by applying a constant potential or passing a constant current through the zinc to cause electrooxidation of a small fraction of the zinc to Zn²⁺ and more rapid formation of the hopeite film. The preferred current density of zinc electrooxidation is not more than about 100 microamperes per square centimeter (cm) and not less than about 1 microamperes per square cm. Alternatively, a chemical oxidant may be added to the phosphating solution. Examples of chemical oxidants include alkali metal chlorates and hydrogen peroxide.

The inventors also consider as important the improvement of the coulombic efficiency of the utilization of zinc in anodes of electrochemical cells, particularly of zinc anodes in electrochemical cells utilizing body fluids as their electrolytes.

The rates, meaning the current densities, of Zn the anodes, for example of those operating in fluids of the body of animals, are generally about 100 microamperes per square cm or less. The electrodes and batteries that may be implanted into a human, mammal, animal, fish, and so forth provide therefore low power for a long period of time, rather than high power for a short period. Generally, the zinc anodes are discharged, when they are in continuous use, over periods longer than about three days. Preferably, the zinc anodes are discharged over periods longer than one week.

When the aqueous electrolyte is a body fluid, the battery case is obviated as long as the materials constituting the anode and the cathode, as well as the reaction products of the two electrodes, are neither toxic nor otherwise harmful. This is so, for example, when the battery is formed of a zinc anode and a silver chloride based cathode. The silver chloride based cathode can be an Ag and/or carbon and AgCl containing paste printed on a plastic film, such as a polyester film, or a chlorided silver wire, overcoated with a harmless, ion conducting, immobile, bioinert hydrogel, as described, for example, by Feldman, et al., in United States Patent Application No. 20050173245.

The zinc anode may, optionally, be subcutaneously implanted, or placed on the skin. It can be used in combination with a cathode that may be also implanted, or it may be on the skin, like an ECG electrode, which usually comprises either silver chloride or an oxide of nickel. Alternatively, an air (oxygen) cathode can be used in the body or on the skin. Such a cathode may include an electrocatalyst for the reduction of oxygen to water, for example, a copper enzyme like bilirubin oxidase, which may be electrically connected through a redox hydrogel to the cathode, typically made of carbon.

The implanted or skin surface cells of the present invention are much smaller than any commercially available battery because they do not require an electrolyte or a case. Their electrolyte can be, for example, interstitial fluid between cells of tissues of the body, peritoneal fluid, blood, plasma or sweat. In one embodiment, the two electrodes (e.g., the zinc anode and the cathode) are inserted in the body, under the skin, in electrolytic contact with a body fluid. In absence of a case or an added electrolyte, the batteries can have volumes smaller than 1 mm³, and even smaller than 0.1 mm³.

In one of its embodiments, the present invention discloses an ion conducting hopeite coated electrode. Additionally, the present invention provides an electrochemical cell, having a cathode and an electrolyte, comprising phosphate and oxygen, in contact with the cathode. The electrochemical cell has a polymer coated zinc anode and a hopeite layer in contact with the electrolyte. The electrolyte may be a body fluid that has phosphate and oxygen, e.g., interstitial fluid. For example, the polymer may be a sulfonate function comprising polymer, exemplified by commercially available NAFION® or by one of the polymers useful, like NAFION®, in membranes separating anode and cathode compartments in acid electrolyte fuel cells, described, for example in U.S. Pat. Nos. 6,423,784, 6,559,237, 6,649,295, 6,833,412, 7,060,738 or 7,060,756. However, the skilled artisan will recognize the layer of hopeite may be formed in a variety of ways, e.g., by a discharge of the zinc anode in a physiological saline buffer. Salts of alkali metal cations, preferably Na⁺ or K⁺, and anions that do not precipitate or strongly complex at about 0.1 M concentration Zn²⁺ are preferred. Examples of useful anions are Cl⁻, Br⁻, SO₄ ²⁻ and NO₃ ⁻. The useful concentration range of the salts is greater than about 50 mM and less than about 3 M, the range greater than about 0.1 M and less than about 1 M being preferred.

One example of the present invention includes an electrochemical cell that is a miniature case-less cell and may be of a variety of sizes depending on the application, e.g., the cell may be smaller than about 30 mm³, between about 20 and about 30 mm³, between 10 and 20 mm³ or smaller than about 10 mm³. The present invention also includes a cell having a hopeite coated anode.

Cation exchanging polymer overcoating of the zinc anodes is of essence for controlling the nucleation underlying the formation of the large non-porous hopeite lamellae (leaves). Other than the exemplary thin a fluorinated sulfonic acid polymer (e.g., NAFION®) film, typically thinner than about 100 micrometers, preferably thinner than about 10 micrometers and most preferably about 1 micrometer in thickness when not swollen in water, films of other cation exchanging polymers may be used to coat the battery anode or the galvanized steel.

The zinc anodes of the body fluid comprising cells may have a variety of different sizes and shapes depending on the application. Other than the exemplary fine (e.g., about 100 micrometer diameter) zinc wire anode, zinc containing films may be printed, painted, screen-printed, evaporated, adhered or sprayed a surface, e.g., plastics, polyester, Nylon sheets, ceramic sheets, woven carbon sheets, non-woven carbon sheets or a combinations thereof. The zinc paints and inks may include a conductive binder, often comprising a polymer with fine graphite or carbon black particles.

Electrolytes may include body fluids (e.g., interstitial fluid, peritoneal fluid, sweat, mucus or blood), and non-toxic, environmentally friendly aqueous solutions. The electrolytes which comprise phosphate (PO₄ ⁻), may also comprise sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), chloride (Cl⁻), and bicarbonate (HCO₃ ⁻). Electrolytes are well known in the art and the skilled artisan will recognize the numerous electrolytes that may be used in conjunction with the present invention.

The pH range of the phosphate containing solution is generally less than about 10 and greater than about 4. It is preferably more than about 5 and less than about 8; most preferably it is between about pH 7.0 and about 7.5. The phosphate concentration range is between at least about 5 mM and less than about 500 mM. Specifically in one example, the phosphate concentration range is between about 10 mM and about 200 mM. The phosphate may be added as an alkali metal salt, such as sodium or potassium salt, optionally a mono or dibasic salt.

Exemplary useful electrolytes include (a) pH 7.4, 20 mM phosphate, 0.05-1 M NaCl; (b) pH 7.4, 20 mM phosphate, 0.5 M NaCl; (c) pH 7.4, 1-100 mM phosphate; 0.03-0.5 M Na₂SO₄; (d) pH 7.4, 20 mM phosphate, 0.05-1 M NaBr; (e) pH 7.4, 20 mM phosphate, 0.05-1.0 M NaNO₃. The importance of solution pH is well known in the art and the skilled artisan will recognize the range of pHs that may be used in conjunction with the present invention.

The present invention includes an electrode having an at least partially conductive substrate having a metal layer on the at least partially conductive substrate. The at least partially conductive substrate then has a polymer coating and a layer of hopeite deposited thereon.

Membranes may be used for controlling the nucleation and morphology of hopeite growth. The useful thickness of the cation exchange membrane, such as NAFION®, is generally greater than 10 nm and is less 500 micrometers. Preferably it is greater than about 0.5 micrometers and is less than about 20 micrometers.

The present invention provides a Zn anode coated with a cation exchanging polymer film, e.g., NAFION®. The coating can formed, for example, by brushing, spraying spin-coating or dip-coating using a solution or suspension or dispersion of the cation exchanger. It is preferred that the resulting film, formed after drying, be of about uniform thickness. The thickness of the useful films is usually greater than about 10 nm and is less than about 100 micrometers. The preferred thickness of the dry films is between about 50 nm and about 1 micrometer. Optionally, the cation exchanging polymer films may be baked on after their drying. When baked, baking at a temperature greater than about 90° C. and less than about 200° C. is preferred, the baking temperature range above about 110° C. and below about 150° C. being most preferred.

In some instances, the at least partially conductive substrate is a metal, (e.g., platinum); however other metals and alloys may be used. The metal layer deposited onto the at least partially conductive substrate and may be zinc, zinc alloys or other metals or metals alloys. The anodes protected can be of different elemental metals and alloys. The protective metal is Zn or an alloy of Zn, for example a Zn alloy with Mg, Al, Ti, Ni, Co, Fe, Y, Yb or Zr. The Zn or its alloy can be applied to the protected metal, such as steel, for example by hot rolling, cold rolling, extrusion, hot pressing, electroplating or dipping in molten Zn or a molten alloy of Zn.

The skilled artisan will recognize the layer of hopeite may be formed in a variety of ways, e.g., by a discharge in a physiological saline buffer. The present invention includes a layer of hopeite deposited in and/or on a polymer coating. Furthermore, the coating may be of a Zn²⁺ conducting inorganic substance other than hopeite. The coating may be used with other subsequently applied films, such as epoxies, enamels and other paints.

Furthermore, the hopeite of the present invention may have lattice substituting ions; the properties of the basic Zn²⁺ ion conductive hopeite phase might be modulated by substituting Zn²⁺ in the Zn₃(PO₄)₂.4H₂O lattice. For example, the modifications may increase the conductivity of Zn²⁺. Potential lattice substituents of Zn²⁺ are divalent, trivalent or tetravalent cations, typically of ionic radii within about ±0.03 nm of the ionic radius of Zn²⁺. They can be, for example, chosen from the group Ni²⁺, Co²⁺, Fe²⁺, Ga³⁺, Y³⁺, Yb³⁺, Bi³⁺, or Zr⁴⁺. In producing the zinc anodes, it might be advantageous to alloy the zinc with one or more of the corresponding metals.

The present invention includes an anode having an at least partially conductive substrate and an external layer of inorganic crystals and in some instances, the inorganic crystals are hopeite. In addition, the present invention provides a method of preparing an electrode by depositing a metal layer onto a substrate, applying a polymer coating layer onto the metal layer and growing a layer of hopeite onto the polymer coating layer.

In some instances, the conductive substrate is a metal (e.g., platinum); however alloys and other combinations metals may be used. The metal layer (e.g., zinc or zinc alloys) is deposited onto the substrate; however, the skilled artisan will recognize that other metals may be used depending on the particular application. For example, the present invention provides a method of preparing an electrode by depositing a zinc layer onto a platinum substrate. A fluorinated sulfonic acid polymer layer is applied to the Zn layer and a layer of hopeite is deposited onto the fluorinated sulfonic acid polymer layer. However, the present invention may be used with other fluorinated polymers (e.g., NAFION®) and a variety of other sulfonic acid copolymers. Although, fluorinated sulfonic acid polymers are used as an example the skilled artisan will recognize that a variety of coatings of polymers and copolymers may be used.

Generally, FIG. 1 shows schematically the process by which the fluorinated sulfonic acid polymer coated zinc electrode 10 was prepared. FIGS. 1A, 1B and 1C are cross-sectional views of a schematic that illustrates the steps of the preparation of the fluorinated sulfonic acid polymer coated zinc electrode 10. FIG. 1A indicates about a 2 cm long and about 76 μm thick (0.031 cm²) platinum wire 12. FIG. 1B illustrates a Zn electrodeposition. The Zn layer 16 is electrodeposition deposited onto the platinum wire 12. Zinc anode 14 was prepared by electro-plating about a 20 μm thick Zn layer 16 on about a 2 cm long and about a 76 μm diameter platinum wire 12 at about 2 mA constant current, in about 1,000 seconds, from about 0.6 M ZnCl₂—2.8 M KCl—0.32 M H₃BO₃—0.3% polystyrene sulfonate and about 2 coulombs being passed. The initial surface area was about 0.075 cm². FIG. 1C illustrates a fluorinated sulfonic acid polymer coating 18 of the electrodeposited Zn 16 on the platinum wire 12. The anodes were coated with a 16 μm thick fluorinated sulfonic acid polymer film, by dipping in about 0.5% (10:1 isopropanol diluted) about 5% fluorinated sulfonic acid polymer and drying.

Cells of about 1.01 V open circuit voltage were formed of the hopeite coated zinc anodes and Ag/AgCl cathodes with physiological saline pH 7.4 buffer containing 20 mM phosphate buffer and 0.15 M NaCl as the electrolyte. The cathodes were much larger than the anodes, making the cell characteristics anode-controlled. To test the cells under conditions of high corrosive loss of anodic capacity, the cells were discharged slowly, at about 1 μA (13 μA cm⁻²), across about a 1 MΩ resistor at about 1 V. When the fluorinated sulfonic acid polymer coated Zn anodes 10 were discharged in the physiological saline buffer, the fluorinated sulfonic acid polymer coated Zn anodes 10 were overgrown by colorless crystals and the diameter of the fluorinated sulfonic acid polymer coated Zn anodes 10 increased from about 152 μm (e.g., Pt wire, about 76 μm; NAFION® about 2×16 μm; Zn about 2×20 μm) to about 485 μm at completion of the discharge.

FIGS. 2A, 2B and 2C are images of the overgrowth on the fluorinated sulfonic acid polymer coated Zn anodes 10 at different stages of the discharge. FIG. 2A shows optical micrographs of the tips of fluorinated sulfonic acid polymer coated about 2 cm long Zn anode 10 in the pH=about 7.4±0.1 physiological buffer (e.g., about 20 mM phosphate, about 0.15 M NaCl) after passage of a charge of about 4 mC. FIG. 2B shows optical micrographs of the tips of fluorinated sulfonic acid polymer coated 2 cm long Zn anode about 10 in the pH=about 7.4±0.1 physiological buffer (e.g., about 20 mM phosphate, about 0.15 M NaCl) after passage of a charge of about 250 mC. FIG. 2C shows optical micrographs of the tips of fluorinated sulfonic acid polymer coated 2 cm long Zn anode about 10 in the pH=7.4±0.1 physiological buffer (e.g., about 20 mM phosphate, about 0.15 M NaCl) after passage of a charge of about 430 mC.

FIG. 3 shows the X-ray diffraction patterns of the precipitate formed in the fluorinated sulfonic acid polymer membrane of the operating Zn anode (bottom trace) and the commercial Zn₃(PO₄)₂.4H₂O (top trace). The X-ray powder diffraction pattern of the crystals overgrowing the fluorinated sulfonic acid polymer shown in FIG. 3 are identical to that of Zn₃(PO₄)₂.4H₂O (Aldrich, Milwaukee, Wis.) and agreed with the data on PDF card #33-1474 for hopeite (International Centre for Diffraction Data, 12 Campus Blvd. Newton Square, Pa. 19073) and with that reported for synthetic hopeite⁵.

FIGS. 4A, 4B and 4C are images of the fluorinated sulfonic acid polymer coated zinc electrode 10. The top images of FIGS. 4A, 4B and 4C are compositions of optical images (e.g., 40× magnification) and the bottom images of the FIGS. 4A, 4B and 4C are electron micrographs (e.g., about 5000× magnification) showing the dimensions and morphologies of the coatings formed at the completion of the discharge on the fluorinated sulfonic acid polymer coated zinc electrode 10. FIG. 4A shows the dimensions and morphologies of the films formed at the completion of the discharge on the fluorinated sulfonic acid polymer coated zinc electrode 10 in about 0.15 M NaCl without phosphate in about 0.15 M NaCl without phosphate. FIG. 4B shows the dimensions and morphologies of the films formed at the completion of the discharge on the fluorinated sulfonic acid polymer coated zinc electrode 10 in pH about 7.4 about 20 mM phosphate buffer without NaCl. FIG. 4C shows the dimensions and morphologies of the films formed at the completion of the discharge on the fluorinated sulfonic acid polymer coated zinc electrode 10 in about 20 mM pH about 7.4 phosphate buffer with about 0.15 M NaCl.

FIG. 5 is an image that shows details of the electron micrograph at 5000× magnification of the non-porous hopeite Zn₃(PO₄)₂.4H₂O lamellae overgrowing the fluorinated sulfonic acid polymer coated zinc fiber anode upon its discharge in pH about 7.4 physiological (e.g., about 20 mM phosphate, about 0.15 M NaCl) buffer.

FIG. 6 is a plot illustrating the time dependence of the potential of the fluorinated sulfonic acid polymer coated zinc electrode 10. The fluorinated sulfonic acid polymer coated zinc electrode 10 was discharged against an Ag/AgCl cathode at a constant current of about 1 μA at about 25° C. in serum. FIG. 6 trace (a) shows the curve for the cell with serum. The fluorinated sulfonic acid polymer coated zinc electrode 10 was discharged against an Ag/AgCl cathode in pH about 7.4, about 0.15 M NaCl, about 20 mM phosphate buffer. FIG. 6 trace (b) shows the discharge curve at about 1 μA for the cell with physiological saline buffer as an electrolyte. The fluorinated sulfonic acid polymer coated zinc electrode 10 was discharged against an Ag/AgCl cathode in about 0.15 M NaCl FIG. 6 trace (c). The fluorinated sulfonic acid polymer coated zinc electrode 10 was discharged against an Ag/AgCl cathode in pH about 7.4, about 20 mM phosphate buffer, without NaCl as seen in FIG. 6 trace (d). With serum, the about 1 V output was steady for two weeks, during which the charge passed was about 1.2 C, corresponding to about 60% efficiency of utilization of the about 2 C utilized in forming the Zn plate. In the physiological buffer, the about 1 V output was steady at for three weeks, and the charge passed was about 1.73 C, corresponding to about 86% Zn utilization. Growth of the non-porous lamellae and high anode utilization efficiency required fluorinated sulfonic acid polymer, phosphate and NaCl. Without phosphate as in FIG. 6 trace (c), the hopeite film could not form and in the absence of NaCl the film was porous and the anode corroded rapidly as seen in FIG. 6 trace (d).

At the physiological pH of about 7.4 the dominant non-Faradaic reaction of Zn is that with dissolved O₂.⁶ The extent to which the flux of O₂ to the surface of the operating anode is reduced defines the current efficiency. That the high anode utilization efficiency resulted from blockage of permeation of O₂ to the active Zn by the hopeite film was confirmed as follows. A set of anodes was prepared by electrodepositing different amounts of Zn on the Pt wires. Upon completion of discharge, the cyclic voltammograms were measured, the potential scanned to about −0.5 V vs. Ag/AgCl, where O₂ is electroreduced even on non-catalytic conductors.

FIG. 7 is a cyclic voltammogram that is indicative of the blockage of O₂ transport to the Zn anode. The fluorinated sulfonic acid polymer coated zinc electrode 10 is about 0.075 cm² anodes with fluorinated sulfonic acid polymer coated and about 2 cm long. The voltammograms of FIG. 7 confirmed that the hopeite film was non-porous and blocked the O₂ permeation. The voltammograms of FIG. 7 are for a set of anodes, differing in their amount of electrodeposited Zn, i.e., (a) 0.00 C; (b) 0.05 C; (c) 0.12 C; (d) 0.20 C, after completion of their discharge, and were obtained in air-equilibrated pH about 7.4, about 0.15 M NaCl, about 20 mM phosphate buffer.

O₂ transport-blocking films are rarely solid electrolytes and are usually highly resistive to passage of ionic currents. Thus, with few exceptions, anodes with O₂ transport blocking films discharge only at high overpotentials. The non-porous lamellar hopeite-overgrown Zn anodes were, nevertheless, discharged with little polarization, even when their overgrowth was 100 μm thick. Measurement of the polarization of a set of identical Zn anodes after their discharge to 0, 10, 25 and 50% depth in the physiological saline buffer solution (Table 1) showed that at a current density of about 0.13 mA cm⁻² the polarization of the half-discharged anodes differed by less than about 50 mV from their polarization at the start of discharge. At about 0.26 mA cm⁻¹, the polarization of the half-discharged anodes exceeded their initial polarization only by about 110 mV, showing that the ionic conductance was at least about 2×10⁻³ S. TABLE 1 illustrates the dependence of the polarization on the state of discharge of the Zn anode* J 0% 10% 25% 50% 0.013 0.01 0.00 0.01 0.01 0.026 0.01 0.00 0.01 0.02 0.065 0.02 0.00 0.04 0.04 0.13 0.04 0.01 0.08 0.09 0.26 0.05 0.06 0.19 0.16 Where *J in mA cm⁻²; half cell potential about 1.01 ± 0.01 V vs. Ag/AgCl; discharged at about 13 μA cm⁻²; all values in V ± about 0.01 V.

FIG. 8 is a structural model of hopeite Zn₃(PO₄)₂.4H₂O. Hopeite, an open-framework hydrated zinc phosphate with intersecting channels, is a known host of neutral organic molecules, as well as cations, resembling in this aspect zeolites. The overgrowth of the fluorinated sulfonic acid polymer coated zinc anode by hopeite lamellae continues throughout the entire discharge period, the size reaching about about 20 μm×about 20 μm×about 1 μm. (e.g., FIG. 5). The continued growth, as long as the supply of Zn²+ lasts, implies permeation of either phosphate and water or Zn²⁺. The hopeite crystal ^(1,7) consists of layers of ZnO₄ tetrahedra, linked by PO₄ groupings. FIG. 8 is a structural model of hopeite Zn₃(PO₄)₂.4H₂O with water channels in which Zn²⁺ can diffuse are seen. Selected hydrogen bonds are shown between H14—O4, H35—O5, H36—O6. Between these two sheets, a crystallographically separate Zn atom, Zn1 is present in octahedrally coordinated units of ZnO₂(H₂O)₄. Two oxygen atoms are shared with two separate PO₄ tetrahedra. The four water molecules form a hydrogen-bonded network. This Zn²⁺ atom site contains vacancies,⁸ is replaceable by Ni²⁺⁹ and by Co^(2+10,11), and is ion exchanged by Li⁺ or Cs⁺. These properties suggest that the lattice permeating ion is Zn²⁺, not phosphate.

FIG. 9 is a schematic diagram of a case-less miniature Zn(NAFION®)—AgCl battery operating in the subcutaneous interstitial fluid. The case-less miniature Zn |electrolyte| Ag/AgCl cell battery 22 includes a Zn anode 24 and an Ag/AgCl cathode 26 that are implanted into the skin 28 of a subject and are in electrical communication through the subcutaneous interstitial fluid. The Zn anode 24 and an Ag/AgCl cathode 26 are connected to contact pads 30 and 32 respectively.

The Zn anode 24 and Ag/AgCl cathode 26 may be implanted individually into the skin 28 at a variety of depths and a variety of distances may separate the Zn anode 24 and a cathode 26 provided electrical communication through the subcutaneous interstitial fluid is maintained. For example, the Zn anode 24 and Ag/AgCl cathode 26 may extend about 0.5 cm below the surface of the skin 28, however, the Zn anode 24 and Ag/AgCl cathode 26 may independently be positioned at other depths, e.g., surface mounted, or penetrate 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0 cm or more into the skin and any fraction thereof, e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9 cm. In addition, the Zn anode 24 and Ag/AgCl cathode 26 may be separated by any distance, provided electrical communication through the subcutaneous interstitial fluid is maintained, e.g., 0.25 cm; however, other separation distances may also be used, e.g., 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0 cm or more and any fraction thereof, e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9 cm.

The Zn anode 24 includes an at least partially conductive layer of Zinc, one or more fluorinated sulfonic acid polymer films (not shown) and an external layer of inorganic crystals (not shown). The inorganic crystals may be hopeite, Zn₃(PO₄)₂.4H₂O, which is an ambient temperature solid phase that conducts Zinc ion (Zn²⁺) and is nonporous and impermeable to oxygen to provide protection of the Zn anode 24 from oxygen and other diffusants.

Hopeite allows about 86% efficient discharge of Zn anode 24 in a physiological saline buffer. In addition, the skilled artisan will recognize that the Zn anode 24 may contain a variety of different elemental metals and alloys, e.g., Zn, an alloy of Zn with Mg, Al, Ti, Ni, Co, Fe, Y, Yb or Zr.

The contact pads 30 and 32 are connected to the Zn anode 24 and a cathode 26 respectively. Although, the connections are illustrated as external contact pads 30 and 32, it is not necessary for the contact pads 30 and 32 to be on the epidermal layer, but contact pads 30 and 32 may be on or in the dermal layer, basal layer, externally positioned on or about an organ, internally positioned to an organ and so forth.

The Zn anode 24 and a cathode 26 are connected through the subcutaneous interstitial fluid of the skin 28. The subcutaneous interstitial fluid may include body fluids (e.g., mucus, blood, sweat, and tears) and/or aqueous solutions. The subcutaneous interstitial fluid acts as an electrolytes and may include sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), chloride (Cl⁻), phosphate (PO₄ ⁻), and bicarbonate (HCO₃ ⁻) and salts (e.g., KCl, NaCl and so forth). The pH range of the subcutaneous interstitial fluid is generally less than about 10 and greater than about 4. In some instances the pH may be as low as about 5 and as high as about 8, e.g., between about pH 7.0 and about 7.5.

For example, case-less miniature Zn |electrolyte| Ag/AgCl cell battery 910, made include a fine Zn fiber anode 24 and an Ag/AgCl cathode 26 may be implanted into the skin 28 to provide about 1.00 V and about 13 μA cm⁻² for about 2 weeks, at about 60% current efficiency.

In combination with the Ag/AgCl cathode, the hopeite-overgrown zinc fiber anode forms a cell with an open circuit voltage of about 1.01 V. Its polarization is merely about 10 mV at about 13 μA cm⁻², and the zinc utilization efficiency is as high as about 86%. With a chlorided silver fiber cathode, overcoated with crosslinked hydrated polyethylene oxide or with another bioinert chloride-permeable hydrogel, ¹² the anode could form a miniature in-vivo cell about a hundredfold smaller than the smallest available battery and could operate at about 1 V for about two weeks.

Alternatively, in combination with an oxygen cathode having a copper enzyme like bilirubin oxidase, the zinc anode would form a cell with an about 1.5 V open circuit voltage operating at about 1.2 V-1.4 V in a buffer with about neutral pH having phosphate and an alkali halide, e.g., NaCl. In combination with an oxygen cathode having a copper enzyme like laccase the zinc anode would form a cell operating at about pH 4-6 with an open circuit voltage of about 1.6 V operating at about 1.3-1.5 V.

The present invention provides a non-porous inorganic lamellar composition including a phosphate anion and one or more metal cations formed on a substrate surface, wherein the non-porous inorganic lamellar composition forms a layer that allows the transport of at least one ion at 25° C.

The present invention also provides a substrate having a first inner metal and a second outer metal. The surface of the second outer metal reacts to form a non-porous lamellar layer that allows the transport of at least one ion at 25° C. The non-porous lamellar layer includes a compound formed of a phosphate anion and one or more metal cations.

A method of surface treating a corrodible metal by coating a corrodible metal with a non-porous lamellar film is also provided by the present invention. The non-porous lamellar film includes an inorganic phosphate of one or more metal cations to form a substantially impermeable film that provides an anticorrosion effect on the corrodible metal.

In addition the present invention provides an electrical power generating electrochemical cell. The electrochemical cell includes an electrolyte providing for ion transport between a cathode and a zinc anode. The anode includes a non-porous inorganic lamellar film of a compound of phosphate and one or more metal cations for the preventing or reducing non-Faradaic corrosion of the anode. In one embodiment the substantially non-porous lamellar film is hopeite and conducts Zn²⁺ ions.

The present invention provides a composition having a cation exchanger coated on a metal substrate and an inorganic lamellar layer formed on the cation exchanger. The inorganic lamellar layer is substantially oxygen impermeable and allows the transport of one or more metal ions. The inorganic lamellar layer includes one or more phosphate anions and one or more metal cations and the cation exchanger influences relative growth of the inorganic lamellar layer. Generally, the inorganic lamellar layer is hopeite; however other inorganic lamellar layers may be used. The metal substrate includes zinc, a zinc alloy and in some instances may be a coating of zinc or zinc alloy on another substrate.

In addition the present invention provides a method of surface treating a corrodible metal by coating a corrodible metal with a cation exchanger and forming an inorganic lamellar layer on the cation exchanger. The inorganic lamellar layer allows the transport of one or more metal ions and that provides an anticorrosion effect on the corrodible metal. The inorganic lamellar layer includes one or more phosphate anions and one or more metal cations and the cation exchanger influences relative growth of the inorganic lamellar layer.

In addition, the present invention provides a method of forming a metal electrode that is protected against non-Faradaic corrosion by immersing a cation exchanger coated metal electrode in a phosphate containing solution and forming an inorganic lamellar layer on the cation exchanger. The inorganic lamellar layer allows the transport of one or more metal ions, with the cation exchanger influencing the relative growth of the inorganic lamellar layer. Generally, the inorganic lamellar layer is hopeite; however other inorganic lamellar layers may be used. The metal substrate includes zinc, a zinc alloy and in some instances may be a coating of zinc or zinc alloy on another substrate.

In addition, the phosphate containing solution may contain other salts including NaCl, KCl and combinations thereof. Furthermore, in animal or human implantable embodiments NaCl, KCl, phosphate and metal ions may be supplied by the fluids and cells of the animal or human implanted therewith.

As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, MB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations can be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

References:

(1) Whitaker, A. Acta Crystallographica, Section B: Structural Crystallography and Crystal Chemistry 1975, B31, 2026.

(2) Mano, N.; Kim, H.-H.; Zhang, Y.; Heller, A. An oxygen cathode operating in a physiological solution. In Journal of the American Chemical Society, 2002; Vol. 124; pp 6480.

(3) Mano, N.; Mao, F.; Heller, A. ChemBioChem 2004, 5, 1703.

(4) Heller, A. Annual Review of Biomedical Engineering 1999, 1, 153.

(5) Pawlig, O.; Trettin, R. Materials Research Bulletin 1999, 34, 1959.

(6) Boto, K. G.; Williams, L. F. G. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1977, 77, 1.

(7) Whitaker, A. Acta Crystallographica, Section B: Structural Crystallography and Crystal Chemistry 1978, B34, 2385.

(8) Hill, R. J.; Jones, J. B. American Mineralogist 1976, 61, 987.

(9) Wu, W. Y.; Liang, X. Q.; Li, Y. Z. Acta Crystallographica, Section E: Structure Reports Online 2005, E61, i108.

(10) Wu, W. Y.; Liang, X. Q.; Li, Y. Z. Acta Crystallographica, Section E: Structure Reports Online 2005, E61, i105.

(11) Rajic, N.; Zabukovec Logar, N.; Kaucic, V. Zeolites 1995, 15, 672.

(12) Tirelli, N.; Lutolf, M. P.; Napoli, A.; Hubbell, J. A. Reviews in Molecular Biotechnology 2002, 90, 3. 

1. A composition comprising: a phosphate anion and one or more metal cations that form a non-porous inorganic lamellar layer on a substrate surface, wherein the lamellar layer allows the transport of at least one ion at 25° C.
 2. The composition of claim 1, wherein the non-porous lamellar layer comprises hopeite.
 3. The composition of claim 1, wherein the non-porous lamellar layer is substantially oxygen impermeable.
 4. The composition of claim 1, wherein the non-porous lamellar layer conducts Zn²⁺ ions.
 5. The composition of claim 1, wherein the non-porous lamellae layer further comprises nickel, magnesium, manganese, calcium, cobalt, copper, magnesium or mixtures and combinations thereof.
 6. A substrate comprising: a first inner metal and a second outer metal, the surface of the second outer metal reacted to form a non-porous lamellar layer that comprises a compound formed of a phosphate anion and one or more metal cations, the lamellar layer allowing the transport of at least one ion at 25° C.
 7. The composition of claim 6, wherein the non-porous lamellar layer is substantially oxygen impermeable.
 8. The composition of claim 6, where the first inner metal is an alloy of iron or copper.
 9. The composition of claim 8, where the alloy of iron is steel.
 10. The composition of claim 6, where the second outer metal is zinc of galvanized steel.
 11. A method of surface treating a corrodible metal comprising the steps of: coating a corrodible metal with a non-porous lamellar film comprising an inorganic phosphate of one or more metal cations to form a substantially impermeable film that provides an anticorrosion effect on the corrodible metal.
 12. The method of claim 11, wherein the non-porous lamellar film comprises hopeite.
 13. An electrical power generating electrochemical cell comprising: an electrolyte providing for ion transport between a cathode and a zinc anode, wherein the zinc anode comprises a non-porous inorganic lamellar film of a compound of phosphate and one or more metal cations, the film preventing or reducing non-Faradaic corrosion of the zinc anode.
 14. The cell of claim 13, wherein the lamellar film prevents, or reduces the rate of, the reaction of oxygen of with the zinc of the zinc anode.
 15. The cell of claim 13, wherein the substantially non-porous lamellar film is hopeite.
 16. The cell of claim 13, wherein the substantially non-porous lamellar film conducts Zn2+ ions.
 17. The cell of claim 13, wherein the electrolyte comprises a body fluid.
 18. The cell of claim 13, wherein the cathode and the zinc anode are implanted in an animal.
 19. A zinc anode electrode protected against non-Faradaic corrosion by an ion conducting inorganic lamellar layer that is formed by passing a current through the electrode immersed in a phosphate containing solution to form a non-porous hopeite lamellar layer on the zinc electrode.
 20. The electrode of claim 19, wherein the lamellar layer comprises hopeite.
 21. A composition comprising: a cation exchanger coated on a metal substrate; and an inorganic lamellar layer formed on or in the cation exchanger that is substantially oxygen impermeable and that allows the transport of one or more metal ions, wherein the inorganic lamellar layer comprises one or more phosphate anions and one or more metal cations, whereby the cation exchanger influences relative growth of the inorganic lamellar layer.
 22. The composition of claim 21, wherein the lamellar layer comprises hopeite and the metal substrate comprises zinc.
 23. A method of surface treating a corrodible metal comprising the steps of: coating a corrodible metal with a cation exchanger; forming an inorganic lamellar layer on or in the cation exchanger that allows the transport of one or more metal ions and that provides an anticorrosion effect on the corrodible metal, wherein the inorganic lamellar layer comprises one or more phosphate anions and one or more metal cations, whereby the cation exchanger influences relative growth of the inorganic lamellar layer.
 24. The method of claim 23, wherein the lamellar film comprises hopeite and the corrodible metal comprises zinc.
 25. A method of forming a metal electrode that is protected against non-Faradaic corrosion comprising the steps of: immersing a cation exchanger coated metal electrode in a phosphate containing solution; and forming an inorganic lamellar layer on or in the cation exchanger that allows the transport of one or more metal ions, whereby the cation exchanger influences relative growth of the inorganic lamellar layer.
 26. The method of claim 25, wherein the non-porous lamellar film comprises hopeite and the cation exchanger coated metal electrode comprises zinc. 